1. Field of the Invention
This invention relates generally to fluid dynamic bearings and more specifically to a fluid dynamic bearing assembly configured with an orbital ring that rotates at a fractional speed, thereby increasing the overall stiffness-to-power ratio of the assembly.
2. Description of the Background Art
Fluid dynamic bearings tend to generate less vibration and non-repetitive run-out in the rotating parts of motors than ball bearings and other types of bearings. For this reason, fluid dynamic bearing motors are oftentimes used in precision-oriented electronic devices to achieve better performance. For example, using a fluid dynamic bearing motor in a magnetic disc drive result in more precise alignment between the tracks of the discs and the read/write heads. More precise alignment, in turn, allows discs to be designed with greater track densities, thereby allowing smaller discs and/or increasing the storage capacity of the discs.
An ongoing challenge in fluid dynamic bearing motor design is balancing the tradeoff between motor performance and power consumption. On the one hand, increasing the stiffness of the fluid dynamic bearings results in less vibration in the motor's rotating parts and, therefore, increased motor precision and performance. On the other hand, however, increasing bearing stiffness results in greater power consumption because of increased viscous losses in the bearings. Conversely, decreasing the power consumption of the fluid dynamic bearings typically requires a substantial decrease in bearing stiffness and, hence, decreased motor performance.
In the field of fluid dynamic bearing motors for use in hard disc drives, bearing designs utilizing an orbital ring on which sets of journal and thrust bearings act in series produce higher stiffness efficiency and higher damping. Such fluid dynamic bearing motors have a number of disadvantages, however, including lower stiffness due to the bearing stiffness acting in series, and up to twice as many precision surfaces to machine and groove.